When your ex boyfriend/girlfriend seems to become extremely less attractive as soon as you stop dating him or her.
Yo have you seen Alexis? Because of the ex effect, she's gotten like a bajillion times uglier in the 14.6 seconds since I've broken up with her.
by PussWrangler October 27, 2013
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A psychological effect, induced by name dropping certain video games, that causes anyone who played that game to have a sudden urge to play it.

Named after the 2000 PC game Deus Ex, which famously will cause at least one person in the conversation to reinstall the game whenever mentioned, especially online.
Fred: Hey man, did you ever play that Deus Ex game? It was totally awesome.
Bill: Oh yeah, I loved that game! I should install it on my new PC.
Fred: Aw man, now I wanna play it!
Bill: That's the Deus Ex effect for you, buddy.
by JD Tenton November 10, 2011
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When a girl makes very noticeable changes to her appearance (ex. dying or cutting her hair, wearing particularly sexy clothes) before meeting up with her ex-boyfriend - who is usually the one who left her - a short period of time after the break up to "grab a coffee" or "get her stuff back". This is supposed to have the effect of a shock for the guy, who feels like he's already missed out on a lot and like she's doing great and moving on without him. The goal is to make him ultimately regret his decision.
We were supposed to go to a cafe today to "talk about it", but I bailed because I want Sarah to dye my hair before the next time he sees me, so that the Ex-Girlfriend Effect is be complete.
by sassanova January 29, 2010
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